a plateau?

I forgot about plateaus (plateaux?). But all week, every physical activity has been a chore. I mean, I can do it, but it feels like it's the hardest thing I've ever done, and I have to completely talk myself into it, and I'm doing okay times, but it still feels like I'm dragging a piano. All week. So, in the hot tub today, after I relayed my woes, Matt reminded me of the concept of "plateau." Could this be it? If so, could it also mean that a *major breakthrough* is on its way (and what would that entail anyway)?

. . . or am I just really tired?

Anyway, it went like this today.
Warmup (400m): the usual. swim, kick, pull, swim.
Technique (400m): 400IM--[kick (stroke specific), swim, drill, swim on each 100m].
Minispeed (700m): 4 x 175 :20 [25 easy, 25 fast, 25 easy, 100 fast]. #1 & #3 kick with board, #2 backstroke, #4 breaststroke.
Anaerobic Threshold (1200m): 12 x 100m free, negative split. First 4 on 1:50, next 8 on 1:55. I tried to work it on 1:50, but was too out of breath! so bumped my pace up :05, which still had me out of breath, but at least I could still go. On the first one, I came in at 1:41. Then 1:43 several times, and managed the second and third last at 1:46, and the very last at 1:45.
Recovery (300m): 3 x 100, 50 breast/ 50 kick (fly/ back).
Warmdown (200m): easy.
===3200m

And seeing that I didn't do my core today (see above, near "piano"), I hereby promise to myself and the ether, that I will do a double circuit tomorrow. Even if it ends up being at 10pm and I think I'm completely exhausted.